1. Field of the Invention
The present invention relates to a handheld scanning subsurface detector, particularly for detecting reinforcements or lines embedded in concrete or masonry, and to an associated control method.
2. Description of the Prior Art
The detection of embedded objects plays an important role in the constructional industry for detecting iron reinforcements, metal pipes, electric lines, or plastic conduits. The detection measurement methods upon which the subsurface detection is based are not the subject matter of the present application and will not be discussed in detail. Generally, embedded objects are detected and identified by changes in the impedance of an impressed magnetic near-field, e.g., according to U.S. Pat. No. 6,541,965, by changes in the impedance of an impressed electric near-field according to WO02063343, or electromagnetically by radar according to U.S. Pat. No. 5,541,965.
Subsurface detectors which scan along a scanning direction depend upon a reliable detection of path differences on wall surfaces which, in the constructional industry, are usually course and rough. By wall surface is meant, within the meaning of the invention, surfaces of walls, ceilings, floors, etc. which are at least partially planar.
U.S. Pat. No. 5,296,807 discloses a subsurface detector of the type mentioned above for embedded, one-dimensional objects and including a handheld measuring head which is movable in a scanning manner over a surface and which includes a detector module for an impressed magnetic nearfield, a path sensor, and a spatially separate image-generating evaluating unit which is connected to the measurement head so as to enable transmission of signals. The four guide wheels of the subsurface detector, which are spaced from one another, are connected in pairs by rigid axles to one another and to the latter by a toothed belt so as to be fixed without a possibility of rotation relative to each other so that the measuring head is always compulsorily guided along a straight line. The path sensor, which is likewise driven by the toothed belt and is constructed as an incremental sensor, is sensitive to the movement of the guide wheels. The spatial data detected by the path sensor and the detection data which are continuously detected by the detector module, are calculated in a separate evaluating unit with computing means and the results are displayed on a graphic display.
According to German Publication DE10207477, a subsurface detector of the type mentioned above and having a detector module and computing means within a handheld housing and a graphic display, is moved back and forth in a scanning manner in one dimension over the to-be-analyzed wall surface. The relative path change is detected along one scanning direction by a path sensor and is processed by the computing means of the subsurface detector. The four guide wheels of the subsurface detector which are spaced from one another are connected to one another in pairs by rigid axles without a possibility of rotation relative to each other. When the guide wheels are lifted, resulting in erroneous measurements, this is detected by the path sensor that triggers an error report that is presented to the user. Nevertheless, detection measurements are still possible when the guide wheels are partially or completely lifted from the subsurface.
It is the object of the invention to realize a handheld scanning subsurface detector which reliably prevents a detection measurement when the guide means are partially or completely lifted off the substrate, and an associated control method.